A number of implantable medical devices have been commercially distributed that allow various medical agents to be controllably infused after implantation of the respective device within a patient. For example, implantable medical devices are used for the infusion of insulin, opiates, anti-spasmodic drugs, intrahepatic chemotherapy agents, and other therapeutic agents in a number of countries subject to the regulatory requirements of those countries.
There are a number of benefits to the use of implantable infusion devices. For example, when the therapeutic agent is delivered directly to the therapy site (for opiates and baclofen), the amount of the therapeutic agent that is needed is much lower. Side-effects are generally minimized. Also, the therapeutic effect can be significantly greater as compared to intravenous introduction of therapeutic agents (again, for opiates and baclofen). Furthermore, implantable infusion devices eliminate patient overdosing or underdosing due to patient error or limited patient capacity.
Implantable infusion devices typically include a central housing that includes a reservoir to hold the infusate, a septum to allow infusate to be introduced into the reservoir, an energy source to drive the infusate from the reservoir and through an outlet port, and various flow control elements. The central housing portion of the device is typically implanted in a suitable subcutaneous region with the septum positioned immediately below the skin of the patient to facilitate access to the reservoir for refilling purposes.
To deliver the infusate from the reservoir, a catheter is usually attached to the outlet port of the central housing to receive the infusate outflow. The distal end of the catheter is implanted within the patient adjacent to the appropriate therapy site (e.g., at a suitable intrathecal location to allow introduction of an infusate directly into the spinal fluid of the patient). Typically, some mechanism is employed to anchor the catheter so that infusate will continue to be delivered to the appropriate site such as sutures and/or anchoring structures.
Similar anchoring is also used in spinal cord stimulation (SCS) systems. In SCS systems, a pulse generator is typically implanted within a subcutaneous pocket within the patient. An electrical lead is also implanted within the patient. The proximal end of the electrical lead is electrically coupled (either directly or via one or more extensions) to the pulse generator to receive electrical pulses from the pulse generator. The distal end of the electrical lead is positioned with electrodes of the lead disposed within the epidural space of the patient to deliver the electrical pulses to the spinal neural tissue of the patient. The efficacy of the electrical stimulation in treating chronic pain of the patient depends upon applying the electrical pulses to the appropriate neural tissue. Accordingly, it is desired to retain the stimulation lead at a relatively fixed position over time. For that reason, the electrical lead is anchored so that migration of the electrical lead does not occur.